Digital x-ray imaging systems are becoming increasingly widespread for producing digital data, which can be reconstructed into useful radiographic images. In current digital x-ray imaging systems, radiation from a source is directed toward a subject, typically a patient in a medical diagnostic application. A portion of the radiation passes through the patient and impacts a detector. The surface of the detector converts the radiation to light photons, which are sensed. The detector is divided into a matrix of discrete picture elements or pixels, and encodes output signals based upon the quantity or intensity of the radiation impacting each pixel region. Because the radiation intensity is altered as the radiation passes through the patient, the images reconstructed based upon the output signals, provide a projection of the patient's tissues similar to those available through conventional photographic film techniques.
In one currently available system, the surface of the digital detector is divided into a matrix of picture elements or pixels, with rows and columns of pixels being organized adjacent to one another to form the overall image area. When the detector is exposed to radiation, photons impact an aluminum/graphite cover coextensive with the image area. The image area is usually coated with a material to prevent the corruption of the detector and moreover to create better quality images. A series of detector elements are formed at row and column crossing points, each crossing point corresponding to a pixel making up the image matrix. In one type of detector, each element consists of a photodiode and a thin film transistor. The photodiode is the photosensitive element that absorbs light from the scintillator and discharges the capacitor. The cathode of the diode is connected to the source of the transistor, and the anodes of all diodes are connected to a negative bias voltage. The gates of the transistors in a row are connected together and the row electrode is connected to scanning electronics. The drains of the transistors in each column are connected together and each column electrode is connected to additional readout electronics. Sequential scanning of the rows and columns permits the system to acquire the entire array or matrix of signals for subsequent signal processing and display.
In use, the signals generated at the pixel locations of the detector are sampled and digitized. The digital values are transmitted to processing circuitry where they are filtered, scaled and further processed to produce the image data set. The data set may then be used to store the resulting image, to display the image, such as on a computer monitor, to transfer the image to conventional photographic film, and so forth. In the medical imaging field, such images are used by attending physicians and radiologists in evaluating the physical conditions of a patient and diagnosing disease and trauma.
Digital x-ray imaging systems are particularly useful due to their ability to collect digital data, which can be reconstructed into the images required by radiologists and diagnosing physicians, and stored digitally or archived until needed. In conventional film-based radiography techniques, actual films are prepared, exposed, developed and stored for use by the radiologist. While the films provide an excellent diagnostic tool, particularly due to their ability to capture significant anatomical detail, they are inherently difficult to transmit between locations, such as from an imaging facility or department to various physician locations. By contrast, the digital data produced by direct digital x-ray systems may be processed and enhanced, stored, transmitted via networks, and used to reconstruct images which can be displayed on monitors and other soft copy displays at any desired location. Similar advantages are offered by digitizing systems, which convert conventional radiographic images from film to digital data.
In digital detectors of the type described above, problems may arise due to corruption of the panel, and more specifically, of the individual components within the detector. For example, moisture may have a corruptive effect upon the components. The amorphous silicon and cesium iodide scintillators are particularly moisture sensitive, and with entry of moisture into the system, system degradation may occur. Proposed solutions to protect such sensitive components include individually coating these materials. However, this process only protects the individual components and only during the manufacturing process. For instance, during shipping the system may be contaminated by moisture. Furthermore, individually coating the components of the system may adversely affect the compatibility of the components with each other.
Another approach to this problem may be to manufacture the detector and system in a clean environment. Although a clean environment provides some protection during manufacturing, such protection is not provided after the manufacturing process. For instance, the housing incorporating the panel and components is not sealed during the process. Therefore, after completion the housing may not adequately protect the internal components of the detector against moisture and other potential contaminants.
There remains a need, therefore, for an efficient and dependable technique designed to seal a digital detector. There is a particular need for a technique which can be implemented to the housing of a digital detector, such that corruption by external contaminants is reduced or prevented, thereby to avoid degradation of a digital x-ray imaging system.